Particle classifiers



July 5, 1960 R. E. PAYNE ET AL PARTICLE CLASSIFIERS Filed June 13, 1957 6 Sheets-Sheet 1 R. E. PAYNE ETAL PARTICLE CLASSIFIERS 6 Sheets-Sheet 2 July 5, 1960 Filed June 13, 1957 1960 R. E. PAYNE ETAL' 2,943,735

PARTICLE CLASSIFIERS Filed June 15, 1957 e Sheets-Sheet :5

. Fig.3 F

July 5, 1960 Filed June 13, 1957 Fig. 4

R. E. PAYNE A PARTICLE CLASSIFIERS 6 Sheets-Sheet 4 July 5, 1960 Filed June 15, 1957 6 Sheets-Sheet 5 United States Patent PARTICLE 'CLASSIFIERS Filed June 13, 1957, S81. No. 665,426 20 Claims. 01. 209-144 This invention relates to improvements in the grading or separation of finely divided material on the basis of size and density, and has for an object the provision of apparatus for effecting a separation at high efiiciency of particle sizes at a selected cut point in the range above about 50 microns.

This invention is an improvement over the one disclosed and claimed in Serial No. 506,826, filed May 9, 1955, which has matured into Patent 2,796,173, granted June 18, 1957.

In accordance with the invent-ion of the aforesaid application, classifier-shave been constructed which operate with high efficiency and high through-put per unit of time with cut points for particle sizes of the order of one micron and above. Where cut points are to be selected within the range of (from about 50 to some 200 microns, it has been determined that the construction of the classifier without consequential loss in efiiciency can be modified for the realization of manufacturing advan tages and to facilitate the inclusion of Wear-resisting surfaces. Accordingly, it is an object of the present invention to provide a classifier particularly adapted to cut points in the range of from 50 to 200 microns, which classifier though of lower manufacturing costand longer life retains the principal advantages of the invention of the aforesaid application.

In carrying out the present invention in one form zone to an intermediate portion thereof where it discharges the finely divided maten'al into the classifying zone. The rotating portion of the one Wall structure is rotated at a speed such that the tangential velocity of the finely divided material enters the classifying zone with a tangential velocity equal to that of the vortex at the location of the discharge region of the inlet means. By thus limiting the rotating portion of the wall structure to that which carries the inlet means, the cost of the apparatus as a Whole is reduced wtihout loss of output per unit of time.

For further objects and advantages of the invention, reference is to be had to the following description taken in conjunction with the accompanying drawings, in which:

Fig. l diagrammatically illustrates a classifying system as a whole and including the improved classifier of the present invention;

Fig. 2 is a sectional elevation with parts shown broken;

Fig. 3 is a plan view with parts omitted to show the air-directing vanes;

Fig. 4 is a plan view partly in section of the classifier of Fig. 2;

Figs. 5, 6 and 7 are graphs explanatory of the invention;

ice

Fig. 8 is a sectional view of a modification of the invention; and

' Fig. 9 is a fractional view of Fig. 8 taken on the line 99 thereof.

.Before discussing the features characterizing the present invention, reference will first be had to the operation as a whole of a typical classifying system together with background theory explanatory of the present invention, as well as that of the aforesaid prior application (United States Patent No. 2,796,173).

Referring to Fig. l, finely divided material from a hopper flows to the classifier 10 by way of, an inlet pipe 11 to a material-feeding valve 12 which forms an air seal for delivering material to a pipe '13 without admission of air. Admission of air to the classifier in mixture, with the finely divided material is regulated by a valve 14 in air-inlet line 15. The finely divided material is separated within the classifier 10. A coarse fraction is withdrawn from a classifying zone by way of a collecting head 16, Fig. 4, a pipe 17, and through a material-feeding valve 18 is discharged to storage. A fine fraction is withdrawn from the classifying zone by way of a collecting scroll 19 and a pipe 20. The fine fraction is delivered to a cyclone separator 21. That portion of the fine fraction separated from the air descends through the collecting cone 21a from which it is discharged by way of a material-feeding valve 22 to storage. It is to be observed that the cyclone separator 21 is provided with an air-outlet pipe 23 which connects to the inlet of a blower 24 which is effective to apply suction to the cyclone separator, and which is also effective to produce forced flow of the air and any fine fraction not removed in the cyclone separator 21 by way of pipe 25 to the classifying zone. A portion of one wall structure of the classifying zone is rotated by a motor 26 which through a variable spsed drive 27 drives the wall structure which is attached to a drive shaft 28 carrying a driving pulley 29, and in manner which will now be described.

Referring now to Fig. 2, it will be seen that the drive shaft 28 has secured to the tapered upper end 28a thereof a distributing cone 30 having a plurality of radial driving vanes 31. 7 Material descend-ing through the pipe '13 is distributed by, and over the area of, the cone 30. The feed material is fed into the spaces between the vanes 31. These vanes rotating with the shaft 28 accelerate the material as it moves outwardly between them. The material from the vanes, now rotating at high speed, moves into channels 33 and flows through them into the inlet openings 34 and into a portion of the classifying zone 10a intermediate the inner and outer boundaries thereof. The

. channels 33 and openings '34, and particularly the regions in which there is a change of direction of the finely divided material, are preferably lined with an abrasionresistance material, such as boron carbide, tungsten carbide, -alumina and the like.

The classification zone 10a is annular and is formed by two wall structures. The upper wall structure 35 is stationary. The lower wall structure 36a36b is inpart stationary and is in part rotatable. The stationary part 36:; extends outwardly from the location of the inlet means 34, while the rotatable part 3611 extends inwardly from the inlet means 34 to and beyond the inner limit r{ of the classifying zone 10a; that is to say, the inner limit r, of the classifying zone 10a is located a substantial distance from the axis of rotation of the shaft 28. The zone 10a extends between the inner limit r, and an outer limit r The arrows associated with the character 10a identify the effective radial limits of zone lfla. The outlet for the fine fraction is formed by the opposing curved surfaces 38a and 39a and of gradually increasing crosssectional area. Thus, the fine fraction from the classifying zone a flows radially inward thereof through the outlet and into the scroll 19 which, as shown in Fig. 1, connects to the outlet pipe 20.

A plurality of vanes 41 located below and adjacent the outer boundary of the classifying zone 10a collectively serve to act as fluid directors to produce within thezone 10a an inwardly spiraling vortex. Air under pressure from blower 24 is supplied to the vanes by way of the pipe 25, Figs. 1, 3 and 4, and scroll 44. To maintain uniformity in flow of the air through the vanes and into vortical flow within the classification zone 1011, the scroll 44, as best shown in Fig. 2, has a gradually decreasing cross-sectional area from its inlet at pipe 25 toward the opposite end thereof.

The incoming air under pressure from the blower 24, Fig. 1, flows into the classifying zone 10a by way of the fluid-directing vanes 41.

The plane view of Fig. 3 best illustrates the manner in which the fluid-directing vanes 41 are disposed adjacent the outer boundary of the classifying zone. It will be observed that these vanes 41 overlap about 50% of their length. The vanes are cut from a great circle annulus to fit the spherical surfaces. They are of constant width, and in conjunction with the spherical surfaces between which they are mounted produce in the classifying zone vortical flow of the air with a substantial radial component. In order for the rotating air stream to pass into the zone 10a in streamlined flow, the annular vanes 42 by reason of the location of their inner edges along a path for streamline flow of the air aid in turning the air for flow into the outer limit of classifying zone 10a in a substantially radial direction. Though the vanes 41 may be adjustable, as shown in the aforesaid prior application, nevertheless it is preferred that they be stationary as illustrated in Figs. 2 and 3.

For cut-points of 50 microns and above, the vanes 41 are disposed at angles which measured from tangent lines at theentrance-ends thereof are disposed from about 20 to 60 in radial directions. Thus, the radial component of flow is quite large as compared with the near-tangential relation required for fine cut-points in the neighborhood of a few microns. As will be later explained, advantage is taken of the need of the high radial component of flow of the entering air.

Finely divided material entering the classifying zone 10a through the inlet means 33, 34 and at that time rotating at the same speed as the vortex is immediately subjected to two opposing forces. The first is the centrifugal force P which tends to move all particles outwardly through the classifying zone 10a. The second, an opposing force, F results from the drag on the particles of the radial component of the air flowing inward- 1y through the classifying zone 10a. If these forces F and E be balanced for particles of a given size, then particles below that size-the cut point-will be moved inwardly because the drag force will exceed the centrifugal force for the particles below the cut point. Thus, these smaller particles, the fine fraction, will be moved inwardly beyond the inner limit r, of the classiiiying zone and will flow with the air around the curved path between the curved surfaces 38a and 39a, Fig. 2, and thence to the collecting scroll 19.

Particles above the selected size will move outwardly under theaction of the centrifugal force which for them will exceed that of the drag force. The larger particles, the coarse fraction, move outwardly and through the spaces between a plurality of annular discs or vanes 42 and against an inclined wall 43. The rotating coarse fraction continues to rotate about the wall 43 which is preferably made of abrasiveresistance material, such as alumina or tungsten carbide. As the coarse fraction rotates about wall 43, it is withdrawn through an opening 45 in that wall, as best shown in Fig. 4, and discharged into the pipe 17.

"In the preferred form'of the present invention, the

axial spacing between the surfaces of the wall structure forming the classifying zone 10a increases from the inner boundary r; of the zone to the outer boundary r thereof.

The following equation sets forth the ideal relationship between the axial spacing h and the distance r from the axis of rotation which will produce the desired variation in the drag force:

where h is the axial spacing at the outer boundary of the classifying zone Paraboloids of revolution satisfy the requirement and may, indeed, be utilized for the surfaces of the classifying zone. However, by providing plane surfaces which represent chords of the paraboloids, a close approximation to paraboloids is achieved and adequately close to achieve the desiredclassification of the particles.

in connection with the spacing of the surfaces, reference may be had to the Hebb Patent No. 2,616,563. However, it is to be understood that the purpose of the present invention is to utilize a substantially free vortex g and not one, as contemplated by Hebb, which may lose tangential velocity by viscous resistance to shear in the vortex; and by interaction with wholly stationary walls of the classifying zone and by entry of finely divided material with zero tangential velocity into the central portion of the classifying zone or by entry of such material with the air through the directing vanes.

In order to secure within the classification zone 10a a substantially free vortex flow, there has been substantially eliminated the interaction of a number of forces 1 tending to slow down or to speed up the free vortex flow,

such for example, as the effect due to powder entering the classifying zone.

Where the cut point is selected for particle sizes above say, about 65 microns, it has been found that relatively satisfactory classification can be achieved without the need of rotating both walls of the classifying zone throughout the radial extent of that zone. Thus, by accelerating the finely divided material so that it enters the classifying zone with the same tangential velocity of the vortex within that zone, there is removed one of the larger factors tending to slow down the rotating mass to depart from a true vortex.

That the foregoing may be accomplished will now be explained in terms of a number of relevant factors. The first'to be discussed will be the shear rate which is a factor concerned with adjoining vortex layers. The shear rate is proportional to the viscous shearing forces between layers. With a fixed separation of the surfaces 35 and 36a-36b, the shear rate decreases rapidly outwardly from the center of the vortex. This fact will now be considered from the mathematical standpoint. It Will be remembered that the equation for a free vortex is:

where k is a constant.

The shear rate is given by the equation:

dUt k 1); d1 r T (3) An inspection of Equation (3) makes self-evident the fact that the shear rate increases as r decreases. Accordingly, by making r fairly large, the shear rate is greatly reduced.

Referring now to Fig. 5, there has been plotted a curve 50 with the radius r as 'abscissae and the tangential velocity v, as ordinates. The curve 50 shows the change in tangential velocity for a free vortex with change of radius. Due to the increase in the shear rate as the radius is decreased, there is not attained the velocity v as the radius becomes small, and the change in the tangential velocity of the vortex follows the broken line curve 51.

is a factor which may be taken as a measure of the excellence of free vortex flow maintained in the classifier. That factor or ratio provides a mathematical statement of the location of the classifying zone outwardly of the axis of rotation. While in the preferred form of the invention, the factor of is preferably about 0.4, very superior results will be achieved with values thereof ranging from 0.2 to 0.9.

Referring to Fig. 6, the curve 52 is similar to the curve 50 of Fig. 5, being plotted against the same units for abscissae and ordinates. In Fig. 6, a classifying zone A has been illustrated as having an inner limit of r an outer limit of r,,,,. The introduction of finely divided material at the feed point occurs at an intermediate radius r For such a classifying zone, the optimum speed of rotation of the boundary surfaces will be one matching at the feed point the tangential velocity v of the free vortex. Accordingly, there may be drawn from the origin the straight line 53. This line or graph 53, while matching the tangential velocity V], at the point r of the free vortex, at other points greatly departs from the tangential velocity of the vortex, being much higher at the outer limit r and much lower at the inner limit r With such a classifier, there will be of necessity interchange of energy between the layers of air of the vortex adjacent the boundary surfaces 35 and 36a--36b at all points other than the feed point 34.

Referring now to a classification zone in accordance with a further aspect of the invention of the prior application and of this application and designated at B, it Will be observed that the inner limit r, of the classifying zone a appears along the flat portion of the graph 52, with the feed point r intermediate the inner limit r, and the outer limit r For the classification zone B, the speed of the surface 36b should be equal at the feed point r; to that of the vortex. Accordingly, the graph 54 in the form of :a straight line from the origin to the point r, may be drawn, only that fraction of that line passing through the classification zone B being shown. This line 54 at the origin--the location of the axis of the shaft 28cJorresponds with the point of zero tangential Velocity and the point 0 from which the radius r is measured. The curve 52 for a higher tangential velocity at the feed point r: will be displaced upwardly. For the higher tangential velocities, the departure of broken line 54 from the curve 52 in the zone B increases.

Advantage is taken of the foregoing facts since with lower tangential velocities, the departure of line 54 from the curve 52 in the zone B decreases. Thus, the rotating surface 36b :of the classifying zone 10a closely approximates the speed of the true vortex between the inner limit r, of that zone and the feed point r Sincethe surface 36a is stationary, the line 54 at the point r, moves downwardly to the abscissae line and outwardly to the outer limit r Throughout the zone B, which corresponds With zone 10a, the departure of even the stationary surfaces 35 and 36a from the tangential velocities is of a lower order than in a zone such as illustrated at A.

As already explained for the higher cut points of 50 microns and above, the tangential velocities are of a lower order. For a cut point of 100 microns and a fixed capacity, V will be about 20 feet per second as contrasted with about 1000 feet per second for a cut point of 2 microns.

Stated differently, if v, were held constant for cut points of 50 microns and above, the centrifugal force F due to the increased size and mass of the particles at the cut point, would be 50 times greater than for particles of one micron. For the larger particle cut points, v, is decreased and the drag force E; is increased by increasing the inclination of vanes 41 in a radial direction. The latter positioning is again emphasized since it may vary from 20 to 60 as contrasted with the range of from 0 to 25 for the lower range of cut points.

In summary, by rotating the surface 36b, concurrently accelerating the finely divided material to the speed of the free vortex at the inlet means at location r,, and introducing the feed at the said speed of said vortex, highly satisfactory classification may be accomplished. By reason of the structural features and location of the zone 10a, just described, any loss of energy to the stationary surfaces of the zone 10a is kept low enough so as not to 'alfect in any practical way the efiiciency of the classifier. The advantages thus realized will be further discussed after the development of further theory of operation.

It will be remembered that the ratio of the radial width Ar of the classifying zone to its spacing from the axis \of rotation is a factor from which may be determined optimum dimensions of significant portions of the classifier. For convenience, that ratio may be determined by using the radial width Ar and the distance r from the axis to the feed point as representative of the spacing of the classifying zone from that axis. Thus, the ratio as applied to zone A may be expressed as follows: a

However, for the zone B, corresponding with the preferred embodiment of the invention By locating the classification zone at a substantial distance from the axis of rotation, not only is the shear rate maintained low and the free vortex flow maintained for a classification zone in the region of B of Fig. 6, but also the effect of the boundary surfaces on the free vortex is substantially eliminated. Thus, both factors are substantially eliminated by the location of the classification zone as outlined above.

The foregoing may be stated differently by saying that r,,, the radius to the outer limit of the classification zone, should be large. In addition, in order that an almost perfect free vortex can be maintained, the ratio of r to r, should he be maintained small. As explained in said prior application, in considering these various factors, two very surprising results were discovered. First, it was found that for any given machine and a selected cut point, the ratio of the pressure drop across the classifier to the powder-handling capacity of the machine is least for a ratio of r to. r, of about 1.5. This will now be shown.

The powdershandling capacity of a given machine is proportional to the volume of air flowing through the machine per unit time, Q. A pressure difierential across the machine, Ap, is required to create the volume velocity Q,

that the zone of reasonably .economical performance .is from 1.2 to :2.7 T 'l Inasmuch as these values of correspond with values of from approximately 0.1 to 1.0, it will be seen again that the small ratio of occurs in the same desirable range for and in the same desirable range for necessary for best operation of the classifier.

.As further set forth in said prior application, the second surprising fact is that the material or powder-handling capacity of the classifier does .not increase as its radial width is increased. More particularly, a classifying zone with equal to 5 will have about the same powder-handling capacity as a classifier with 1 equal to 1.5. r

In constructing a classifier embodying the present mvention, it will be useful to maintain the quantity is from 2.5 to 3.5, a range somewhat higher than the preferred range of said prior application.

It may be further observed that the capacity of the machine may be increased by increasing t Since the capacity of the machine theoretically increases as the cube of r a classifier with a capacity of about tons per hour of finely divided material will have a radius r equal to about 20", while a classifier for about 5 tons per hour will have a radius r of about 16 inches.

Since from all of the above considerations, r is preferably large, the forces developed as a result of the required high speeds of rotation are of large magnitude.

In accordance with the present invention, the forces developed are in respect only to the dimension r; and not to r The feed point, r,, is intermediate r and r, and can be somewhat nearer r than r rather than exactly halfway between As best seen in Fig. 2, the rotating assembly is of greatly simplified construction. Though shown as of two-piece construction, i.e., the conical'distributing member 30 and the remaining structure, in practice a lower member 60 will be separately fabricated with the channels 3 3 and openings 34. The open channels greatly facilitate the placement therein of wear-resistant liners mating with the liners for the inlet feed means 34. The upper rotating member 61 along its inner surface forms part of the material-distributing chamber. Its outer surface at 36b forms part of the classifying zone 10a and at 38a it forms one of the surfaces of the rapidly area-increasing exit passage for the fine fraction.

In a region spaced inwardly from the feed point 34, there is provided a flat surface to which there are secured ring elements to form a seal 62. The ring elements have knife edges which ride in grooves disposed within the annular grooves in a stationary member 63. Secured .to or integral with rotating member 61 are upwardly extending skirts, the first 61a being frusto-conical and the second 6117 being cylindrical. An additional seal 64 includes ring elements secured to lower member 60 and nesting within grooves of a stationary member 65. Any air which leaks past the seals 62 and 64 moves radially outward and counteracts any tendency for the finely divided material to move between the moving parts. An. overhanging skirt 66 protects the space between the inner edge of member 63 and rotating member 6111 from ingress of foreign material. A similar seal 61s is provided between rotating member 61b and stationary pipe 13.

Since the sub-assembly of which member 61 is a part is separate from the member 66, it will be seen the curved surface 38a may include a continuous liner of wearresistant material. Similarly such material may be secured to the upper and lower surfaces of member 66 to resist wear.

In addition to the foregoing features, the stationary assembly is mggedly constructed, a torus 67 of steel forming the central supporting member. The torus 67 has welded or otherwise secured to it the stationary member 65, which maybe secured to a frame symbolically represented at 68 in Fig. 1. The torus 67 in the region of the outer limit of the classifying zone forms a part of it as well as the curved surface with which the directing vanes 41 are associated. The outer member forming the scroll 42 is also torus-shaped with a section cut away along the upper portion as viewed in Fig. 2.

As illustrative of the dimensioning of a classifier embodying the invention, r may have the previously given value of 20''; r, a value of about 13%", with r, half-way between or somewhat nearer r than r,,; 11 a value of 2 /2 and h a value of 1 /8". Between the opposed surfaces 35 and 36a, 3612 the spacing gradually increases from about 1%" to a value of approximately 2 inches.

The increase in the cross-sectional area for the flow of air in mixture with the fine fraction from r into the scroll 19 is effective to convert velocity into pressure and is effective in minimizing the pressure drop which occurs between the inlet at the mouths of the directing vanes 41 and the outlet at the suction entrance of blower 24.

If the cut point is to be reduced, say from microns, to increase the fineness of the particles carried by the air inwardly through the classifying zone, the rotational speed of the air and of the particles may be increased. This can be readily accomplished by changing the direction of the curved vanes 41 to direct the air into the outer boundary of the classifying zone in reduction of the ratio of the radial component to the tangential component. Inasmuch as this increases the rotational speed of the air at the outer limit of the classifying zone for a fixed volume of air flow, it is necessary or highly desirable to increase the speed of the shaft 28 to a point where thefinely divided material is positively driven to have aktangential velocity equal to the tangential velocity of air at the feed point 34.

In connection, a tachometer is preferably utilized to measure the speed of the shaft 28. The relationship between the speed of shaft 28 and the setting or angular disposition of the directing vanes 41 may be readily determined by measuring the speed of air in vortex flow within the zone 100. With the tangential velocity of the air at feed point 34 known, the shaft 28 is rotated at a speed to bring the powder entering through the inlet 34 to the same tangential velocity.

If it is desired to increase the' cut point to decrease the fineness of the particles carried inwardly through the classifying zone, the reverse procedures are utilized. Vanes 41 with a greater radial component are used to increase the ratio of the radial component to the tangential component. By thus increasing the drag force relative to the centrifugal force, particles of sizes greater than before move inwardly through the classifying zone 10a. Acorresponding change in the speed of shaft 28 is, of course, made. It will be seen that by varying the ratio of the tangential component to the radial component of the air entering the classifying zone, the cut point may be selected over a wide range, for example, from about 50 microns upwardly was high as 200 microns for finely divided material having a specific gravity of-about 3.0. It is to be noted that the separation depends upon the product of particle diameter and the square root of the specific gravity. Consequently, a larger cut point range will be achieved at lower specific gravities and a smaller cut point range will be achieved at higher specific gravities. Of course, a wider range of cut point can be achieved with some sacrifice in classifying efficiency.

In accordance with the principles of the invention as outlined above, a classifier with approximately twice the output may be constructed without a corresponding increase in the cost of constructing the same. In the classifier 70 of Fig. 8, there are provided two classifying zones 70a-yand 70b, each corresponding in radial position from the axis of the drive shaft 28 and in other respects with the classifying zone 10a of the preceding modification. As in the preceding modification, finely divided material enters by way of the feed valve 12 and the pipe 13. The cone distributor 30 having the radial vanes 31 accelerates the material to be'classified to a rotational speed which at thefeedpoint of each zone corresponds with that of the tangential velocity at the feedpoint of the vortex within each said classifying zone. At the periphery of the vanes 31*, the material divides. Each stream concurrently flows through outlet passages 71a and 71b. The passages 71a and 71b are in staggered relation about the periphery of the cone distributor 30, as shown in the fractional view of Fig. 9 taken on the line 9-9 of Fig. 8. The passages 71a and 71b form a part of the rotating assembly. They are lined with wear-resisting material. They continue the acceleration of the feed material and terminate in openings 72a and 72b corresponding with the feedpoints and respectively spaced from the axis of shaft 28 by the distances r 'As shown, they have the same spacing, but some variation may be included if desired.

The two streams of material to be classified enter the classifying zones 70a and 70b at tangential velocities corresponding with those of the vortex produced in each of the classifying zones 70a and 70b. A scroll 73 generally corresponding with the scroll 44 of the preceding modification is provided for the inlet air. Inlet air passing by way of the directing vanes 74a is directed into classifying zone 70a and by vanes 74b is directed into the classifying zone 70b. Outwardly of the classifying zone 70a is an inclined Wall 75a having annular flow-directing elements 7611 which serve the double function of directing into radial flow the rotating air entering the classifying zone by way of the vanes 74a. Zone 70b is provided with a like construction, the corresponding parts being respectively 75b and 76b. As in Fig. 4, there is 10 an openingin each of inclined walls 75a and 75b for the coarse fraction passing between the annular elements 76a connecting with a discharge pipe 77.

The fine fraction from zone 70a moves inwardly of the classifying zone through the diverging outlet and into a collecting scroll 78a. Similarly, the fine fraction from zone 70b moves into a collecting scroll 78b. The two scrolls are joined together for passage of both fine fractions into separating means (shown at 21, Fig. 1) for withdrawal of the fine fraction and for return of air by way of the blower (shown at 24, Fig. l) to the classifier 70. The seals 80, 81 and 81s function in the same manner as described for seals 61s, 62 and 64 of the preceding modification, it being noted that the number of seals is not increased, notwithstanding the fact the classifying zones have been doubled in number.

As in the preceding modification, the stationary portion of the classifying zone lends itself to a rugged construction which, in part, includes hollow structural members 82 which encircle the axis of shaft 28 and which perform the double functions outlined in connection with the toroidal-shaped member 67 of the preceding modification and in cooperation with both of zones 70a and 70b; While members 67 and 82 of Figs. 2 and 8 are toroidsin that they are surfaces of revolution (i.e., generated by rotating their cross-sectional areas about a central axis, as that of shaft 28), it is to be understood their cross-sectional areas need not be defined by circular or oval-shaped lines, or to conform with conic sections. They may have straight sides. The members 67 and 82 will be continuous in their encirclement of the classifying zone, preferably in the region of its outer limit. These members have. been shown as tubular, i.e., hollow, but they may be solid and formed from round or rectangular rod-stock. In Fig. 8, the oval-shaped cross-sectional areas of members 82 provide a greater area for the air-flow passage formed between the concave inner surface of the outer member forming the scroll 73 and an inner member 73a. The outer member is an annular segment of a toroidal-like member extending between zones 70a and 70b. The elements 760 and 76b have their inner edges located approximately on extrapolations of the concave surface of the outer member of the scroll 73 opposite zones 70aj'and 70b to serve as air-directing elements.

When it is considered that material is to be classified at the rate of from-50 tons to tons per hour, the importance of the several features of the invention and the manner in which they cooperate together will be better appreciated.

What is claimed is:

l. A classifier for finely divided material comprising boundary means including first and second opposing wall structures forming between them an annular classifying zone, means including fluid-directing members adjacent the outer limit of said zone for producing within said zone an inwardly spiraling vortex, inlet means carried by at least one of said wall structures and extending into communication with said zone at a feedpoint intermediate its inner and outer limits, said boundary means being in part stationary and in part rotatable, said rotatable part including said inlet means, said stationary part including at least a part of both said wall structures and extending inwardly from said outer limit of said zone, means for feeding finely divided material to said inlet means, and means for driving said rotatable part including said inlet means at a speedfor delivery of said finely divided material into said classifying zone with a tangential velocity approximately equal tothat of said vortex at said feedpoint. i g

2. The classifier of claim 1 in which the axial distance between the opposing wall structures increases progressively outwardly from the inner limit of the classifying zone to the outer limit thereof.

3. The classifier of claim 2 in which the axial distance it between the opposing wall structures at any radial distance r froin the axis of rotation bears within practical approximation the following relationship:

where h is the axial spacing between the wall structures at the outer boundary of the classifying zone and p is the radius from the axis of rotation to the outer boundary of-the classifying zone. 7 I U 4. The classifier of claim 1 in which said rotatable part includes only that portion of the one of said wall structures carrying said inlet means and extending from said inner limit to the region of said inlet means. c c

5. The classifier of claim 4 in which an outlet passage is provided at said inner limit of said zone, 'sa id rotatable part forming a rotatable surface for a portion of said outlet passage along which said fine fraction flows from said zone. 1 p c I a 6. The classifier of claim 1 in which there are provided two supporting members in the form of hollow toroids of difiering diameter and one within the other. I

7. The classifier of claim 6 in which said toroids are secured together in eccentric relation one to the other.

8. The classifier of claim 6 in which said toroids are secured together in eccentric relation one to the other to provide an annular path for flow of air into said zone, and an entrance for flow of air into the space between said toroids, the cross-sectional area of said space gradually decreasing as the distance from said entrance increases.

9. The classifier of claim 1 in which there are provided an inclined annular outer wall in opposing relation to said classifying zone to receive therefrom a coarse fraction, said fluid-directing members being vanes disposed between said outer limit and said inclined outer Wall and extending in a direction away from said zone, and a plurality of annular fluid-directing elements extending from said outer wall, the inner edges of said elements having differing radial spacings for guiding into radial flow rotating air delivered by said directing vanes.

10. The classifier of'claim 1 in which said fluid directing members are vanes disposed between the opposing surfaces of two toroidal supporting members one of which nests within the other, said opposing surfaces forming an annular fluid-inlet pasage to said zone, said passage having walls curved toward and in a partly radial direction of said zone. a

11. The classifier of claim 10 in which an annular outer Wall is disposed in opposing relation to said zone, said outer wall from said passage being inclined toward said zone and annular fluid-directing elements extending inwardly of said outer Wall toward said zone, the inner edges of said elements terminating at distances approximately corresponding with an extrapolation of the concave inner surface of the outer one of said toroids.

12. A classifier for finely divided material comprising first and second opposing wall structures forming between them an annular classifying zone, means including fluiddirecting members adjacent the outer limit of said zone for producing within said zone an inwardly'spiraling vortex, inlet means extending through a first of said wall structures into communication with said zone at a feedpoint intermediate its inner and outer limits, said second of said wall structures being stationary, said first of said wall structures being in part rotatable and in part stationary, said rotatable part extending from said inner boundary at least to the location of said inlet means and said stationary part extending inwardly from said outer limit, means for feeding finely divided material to said inlet means, and means for drivingsaid rotatable part of said first wall structure at a speed for delivery of said finely divided material into said classifying zone with a 1'2 tangential velocity approximately equal to that of said vortex at said feedpoint. v

13. The classifier of claim 12in which an outlet passage is provided at said inner limit of said zone, 'said rotatable part forming a rotatable surface for a portion of said outlet passage along which said fine fraction flows from said zone. I r

14. The classifier of claim 12' in which there are provided two supporting members in the form of hollow toroids of differing diameter and one within the other.

15. The classifier of claim 14 in which said toroids are secured together in eccentric relation one to the other to provide an annular path for flow of air into said zone, and an entrance for flow of air into the space between said toroids, the cross-sectional area of said space gradually decreasing as the distance from said entrance increases.

16. The classifier of claim 12in which said fluid-directing members are vanes disposed between the opposing surfaces of two toroidal supporting members one of which nests within the other, said opposing surfaces forming an annular fluid-inlet passage to said zone, said passage having walls curved toward and in a partly radial direction of said zone.

17. The classifier of claim 16 in which an annular outer wall is disposed in opposing relation to said zone, said outer wall from said passage being inclined toward said zone and annular fluid-directing elements extending inwardly of said outer wall toward said zone, the inner edges of said elements terminating at distances approximately corresponding with an extrapolation of the concave inner surface of the outer one of said toroids.

18. A classifier for finely divided material comprising boundary means including first and second opposing wall structures forming a pair of annular classifying zones spaced one from the other means including fluid-directing vanes adjacent the outer limit of each said zone for producing within each said zone an inwardly spiraling vortex, inlet means for each of said zones and carried by at least one of said wall structures, said inlet means extending into communication with its respective zone at a feedpoint intermediate its inner and outer limits, said boundary means being in part stationary and in part rotatable, said rotatable part including said inlet means and extending from said inner limit of each said zone at least to said feedpoint, said stationary part extending inwardly from the outer limit of each said zone, means for concurrently feeding finely divided material into both of said inlet means, and means for driving said rotatable part including both of said inlet means at a speed for delivery of said finely divided material into said classifying zone with a tangential velocity approximately equal to that of each said vortex at each said feedpoint.

19. The classifier of claim 18 in which two supporting members of toroidal shape are located at the outer limits of said zones, a third supporting member in the shape of an annular segment of a toroid extending between said zones and outwardly of said two toroids, said vanes for each of said zones being disposed respectively between one of said toroidal shaped members and the concave inner surface of said third supporting member.

20. The classifier of claim 19 in which said third supportingtmember has a fluid-inlet opening between said vanes for admission of fluid, by way of said vanes; to said zones, and guiding means for the fluid issuing from said vanes for directing it radially into each of said zones.

References Cited in the file of this patent UNITED STATES PATENTS 2,796,173 Payne et al. June 18, 1957 

